The invention relates to a blade guide for a device for dispensing paper pieces, with a rotatable roller provided with a slit and over which a paper web is conveyed, and with a blade which is arranged on a carrier pivotable inside the roller and which is outwardly moveable through the slit for a part of the rotation of the roller for forming a tear-off perforation in the paper web.
Such devices, which are used in particular as paper towel dispensers in sanitary facilities, are known, for example, in different embodiments from DE-A 28 14 792. In FIGS. 12 and 13 of the DE-A document, the blade projects approximately perpendicularly from the carrier, wherein, when viewed from an end face, an overall hook-like shape is produced. The carrier is composed of two arms which are pivotally mounted close to the peripheral wall of the roller, respectively in an end wall of the roller, about a common axle which, viewed in the direction of rotation, lies in front of the slit. When the roller is rotated, the blade moves in an arc of a circle through the slit, wherein the carrier lies either on a stationary plate cam or is driven by a crank arm which is mounted on a stationary axle parallel to the roller axle. FIGS. 10 and 11 of DE-A 28 14 792 show an embodiment in which the blade is rotatably mounted on an axle parallel to the roller axle and, guided by the slit in the roller wall, is rotated about the axle. Because of the axle spacing, the blade then projects out of the roller over a part of the revolution of the roller.
The blade guide according to DE-C 36 90 545 includes a carriage which can be displaced into a diameter of the roller, on which carriage the blade is arranged parallel to the direction of displacement and moves outwardly through the slit in a straight line.
According to the strength and elasticity of the paper web to be cut, which is guided over a feed-in press roller, the blade roller and a feed-out press roller, it may happen that the blade does not cut through the paper web, but instead only lifts it from the blade roller. The object of the invention is therefore to provide a blade guide by means of which the blade additionally tensions the paper web in the direction of the periphery of the roller such that perforation does actually take place.
In accordance with the invention, in a first embodiment this can be achieved in that the blade is linked onto the pivotable carrier, and can be moved in a slideway. In an equally advantageous alternative, the object can be solved in a second embodiment in that the blade is linked to two carriers pivotable about parallel axes.
Both embodiments are based on the four-bar linkage principle, in which the blade forms the connecting element, wherein in the first embodiment, a second pivotable carrier is replaced with a joint which is displaceable in the slideway. In this way the cutter blade can be provided with a movement other than a straight one or an arc of a circle about the pivot axle of the carrier, which at first makes it possible for it to be pushed out an angle which causes the teeth of the cutter blade to grip the paper web, and it then inclines in the direction of the periphery of the roller, wherein the paper web is tensioned such that even when the paper web has a high degree of elasticity and strength, the teeth penetrate it and perforate it.
Preferred embodiments propose that the slideway is configured in an arc of a circle, wherein the radius of the slideway is different from the radius of the pivotable carrier, or that the two pivotable carriers form parallelogram rods.
During one rotation of the roller, in a first part of the revolution of the roller, which covers an angle of rotation of, for example, 240xc2x0, the blade is pushed out and then withdrawn again, and in the remaining second part of the revolution of the roller, which covers the remaining angle of rotation of, for example, 120xc2x0, remains withdrawn. In a preferred embodiment, this is achieved in that the pivotable carrier is guided along a fixed curved path which is not in the shape of an arc of a circle.